Overload glitch (Halo 3)
From Halopedia, the Halo wiki
To overload the game in Halo 3 first start a forge game. Become the forge monitor and create a trip mine while making sure to set the minimum run time the same as the maximum run time. This will allow you to have infinite trip mines. Stand over the spawn and start dropping trip mines. After the pile gets quite large (20+ trip mines) blow the pile up. You will know if it has worked because the grav lifts won' t work and the guardians on sandtrap and snowbound. It will also stop the energy shields on snowbound to stop working. While the map is overloaded it can be very glitchy so overloading a map can lead to many other glitches.